The invention relates to a process for the hot press moulding of moulded articles, such as internal linings of motor vehicles or the like, in which planar blanks of tangled fibre mat fleece mixed with binder are permanently shaped with at least one mould, in a multidimensional moulding process following the steam treating of the mat fleece and in which for the shaping process a stabilizing support is introduced at least on one side between the shaping surface of the mould and the mat fleece.
Research concerning the manufacturability and characteristics of simple chip moulded parts, in which the blanks are shaped to give angular multidimensional bodies, particularly where relatively extensive deformations are desired, have revealed that displacements of the chip structure are not uniformly distributed over the entire cross-section during the shaping or deforming process, i.e. there are points of greater thinning and/or greater thickening. In order to eliminate such shaping disadvantages which considerably reduce the quality of the article to be moulded and possibly even make it unsuitable for use, it is already known to cold preshape the blank in a pressing means and to associate with it an elastic support surface, which as a stabilizing support leads to a better distribution of the deforming strain over the chip structure. In this connection the stabilizing support was constituted by a rubber covering (Klauditz, Stegmann, Kratz, Brunswick Technical University, Bericht 90/1965, Westdeutscher Verlag Cologne and Opladen 1965).
The support of the blank which is to be moulded with a press mould using an elastic support surface is the general prerequisite for producing moulded articles with relatively marked three-dimensional deformations when using a material having limited compressability and stretchability, such as a loose chip structure or a binder-mixed tangled fibre fleece.
The industrial transfer of this known process to the continuous moulding of fibrous fleece material to moulded articles with maximum speed characteristics has revealed that the rubber coverings are unsuitable for permanent operating conditions, because, as a result of their relatively smooth surface, they do not ensure an adequate transfer of the deformation forces which occur to the fibrous fleece or non-woven fabric and in the case of extension or elongation distribution of the rubber covering does not or does not always correspond to what is required in the finished part.
In a known apparatus in which the shaping partial surfaces of at least one mould half of the hot press mould act jointly on at least one elasticly deformable, through intermediate layer in such a way that the shaping forces are transferred throuqh said intermediate layer to the non-woven fabric, assistance is provided in that the elastically deformable intermediate layer is wholly or partly roughened on the surface in contact with the nonwoven fabric, or has a surface structure such as is e.g. obtained in the case of fabrics formed from elastic threads of appropriate strength and mesh width. Thus, the transfer of the elongation movements of the elastic intermediate layer to the non-woven fabric during the closing of the mould gives an ideal frictional engagement between the elastic intermediate layer and the tangled fibre fleece or non-woven fabric, both at points with relatively strong deformation and also over the entire surface of the mould (German Pat. No. 27 59 279).
However, it has been found that in the mass production of moulded articles, such as e.g. those used for the internal lining of motor vehicles, there is a relatively early fatigue to the intermediate layer material, so that it has to be replaced and thrown away, particularly if cloth is used as the intermediate layer.
Finally, an apparatus for producing moulded articles from binder-mixed, particulate materials is known, which makes use of a substantially elongation-free stabilizing support in the surface direction (DE-AS 27 13 527). Also in conjunction with this apparatus, the special difficulties when using a stabilizing support were recognized, particularly in that in the case of multidimensional deforming processes during the hot pressing process the material displacement is difficult to absorb, if the materials to be pressed are not able to adequately take up the tensile forces, such as is the case with blanks from mat fleeces of the type of interest here. This problem can only be obviated to a limited extent by a substantially elongation-free stabilizing support in the surface direction and it is particularly disadvantageous that such stabilizing supports, as a result of their freedom from elongation, undergo such a marked deformation even when used once, that they become unusable for a further pressing process even after a very short period of use.
Since for handling reasons these stabilizing supports must be given a relatively stable construction, there short life makes production much more expensive. A further disadvantage of stabilizing supports is that, in order to ensure a good tension transfer to the mat fleece to be shaped, they must have a corresponding surface structure (cloth,burls). Thus, as a deforming aid, they can only be used for deformation and shaping, but not for any other purpose. Prior to the final hot press moulding and compression of the fibre mats they must be removed, because otherwise they would give rise to corresponding marks on the moulded article surface and these are generally not desired.
Another possibility of stabilizing the shaping process in the case of tangled fibre fleeces can be the incorporation into the fleece of a firm fabric. However, this also results in important disadvantages. The fabric embedded in the fibre fleece mats is only reached by the tensile forces of the deformation if they have already been transferred to the fibrous material by the shaping mould surfaces. This generally leads to premature damage in the structure of the fibre mats before the stabilizing fabric insert can come into action.
Tests carried out with more suitable stabilizing supports as an intermediate layer during the deformation process between the shaping surface of the hot press mould and the fibrous material to be pressed have also lead to disadvantages due to the marked stressing due to the male mould pressure, particularly when producing highly curved, three-dimensional moulded articles. As a result the stabilizing supports are rendered unusable after a very short period of time, which is unacceptable for mass production purposes, so that they frequently had to be replaced.